Various contact probes have been used for testing printed circuit boards and electronic devices, and a typical conventional contact probe consists of a tubular sleeve called as a receptacle, a needle member slidably received in the receptacle with its pointed end projecting from one end of the receptacle, and a compression coil spring applying an outward urging force to the needle member. Since such contact probes are required to be used on integrated circuits and other high density electronic devices, they are desired to have extremely small diameters sometimes in the order of hundredths of a millimeter.
FIGS. 13 and 14 show a typical conventional contact probe 101. A receptacle 103 formed of a metallic tubular member is passed through and fixedly secured to an insulated base board 102, and a barrel 106 consisting of a tubular member which is substantially enclosed at its base end is detachably fitted in the inner bore of the receptacle 103. The barrel 106 receives a needle member 107 in axially slidable manner. The needle member 107 is urged towards the open free end of the barrel 106 by a compression coil spring 109 which is interposed between a head 108 provided in the base end of the needle member 107 and the closed end of the barrel 106, and an annular constricted part 110 of the barrel 106 engages the head 108 so as to define the extent to which the needle member 107 can project out of the barrel 106.
The receptacle 103 is provided with a large projection 104 which engages the closed end of the barrel 106 to define the extent to which the barrel 106 may be fitted into the receptacle 103. The receptacle 103 is also provided with a smaller projection 105 which resiliently and frictionally engages annular groove formed around the outer circumferential surface of the barrel 106 to define the aforementioned annular constricted part 110.
Thus, when the barrel assembly 111 consisting of the barrel 106, the needle member 107 and the compression coil spring 109 is fitted into the receptacle 103 as illustrated in FIG. 14, the barrel assembly 111 can be locked in place in the receptacle 103 in a detachable manner.
However, it is desired to reduce the diameter of the contact probe as much as possible as a large number of such contact probes are required to be arranged in the insulated base board 102 of an automated testing machine, which is not shown in the drawings, in a highly dense manner, and it becomes increasingly difficult to ensure a sufficient spring force acting upon the needle member as the wire diameter and the coil diameter of the compression coil spring 109 in the barrel 106 are reduced. Therefore, according to this conventional contact probe 101, it was difficult to ensure a sufficient spring force and a sufficient mechanical strength to the needle member as the density of the contact probes is increased and the overall outer diameter of each contact probe is reduced.
Furthermore, since there is a relatively large number of separate component parts involved in the electroconductive path between the needle member 107 and a lead wire 112 which is typically connected to the base end of the receptacle 103 by way of a plug 113 press fitted thereinto.
It is also desired to be able to easily replace the needle member so as to simplify the manufacture and maintenance of the contact probe. When the entire contact probe is to be replaced, it is desired to be able to readily disconnect the lead wire and reconnect it to a new contact probe.